The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

This curious, round temple is the oldest still-standing marble building in Rome.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Throughout this shopping mall are medieval ruins that were discovered during the mall's construction.

The first museum in the world devoted to sexual gadgetry.

Macabre astrological automaton clock dating to the late 1400s.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

Underneath the city that invented pilsners are a series of historic tunnels that have been storing beer for centuries.

The bridges portrayed on EU currency aren't fictional anymore.

A maze of crosses marks the jumbled divide between the Netherlands and Belgium.

This historical Netherlands fortress still bears the marks of its single siege.

Incredible labyrinth of man made caves.

A beautiful maze marks where three countries meet.

Go inside a revolutionary, cage-less zoo where 70 species of monkeys roam free alongside their human visitors.

This large open-air museum showcases the ordinary lives of the people of the Netherlands and pre-industrial crafts and practices.

Mosaics created from 11 million cigar bands.

Oldest Museum of the Netherlands is a true cabinet of curiosities.

Birthplace of the "Cat in the Cradle" and a cluster of iconic, original windmills that let the Dutch tame the seas.